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Background and aims: Expression of inducible nitric oxide synthase(iNOS) is gr eatly upregulated in the colonic mucosa of patients with collagenous and ulcerat ive colitis. As the transcription factor nuclear factor κB (NFκB) is a major i nducer of iNOS gene expression, we compared activation and transcriptional activ ity of NFκB in colonic mucosal biopsies from these patients. Patients: Eight pa tients with collagenous colitis,six with relapsing ulcerative colitis, and eight with uninflamed bowel were studied. Methods: NFκB DNA binding activity was ass essed by electrophoretic mobility shift assay and inhibitor of NFκB (IκB) kina se (IKK) activity by immunocomplex kinase assay. In vivo recruitment of NFκB to the iNOS promoter was determined by chromatin immunoprecipitation analysis and transcriptional activity by NFκB gene expression profiling arrays. Cells showin g NFκB activation were identified by immunohistochemistry. Results: In collagen ous and ulcerative colitis, as opposed to uninflamed bowel, IKKβactivity and st rong NFκB DNA binding gave rise to activation of identical NFκB subunits and r ecruitment of transcriptionally active p65 to the iNOS promoter. In collagenous colitis,activated NFκB was observed only in epithelial cells while up to 10%of lamina propria macrophages showed activation in ulcerative colitis. Conclusions : In collagenous and ulcerative colitis, colonic mucosal NFκB is activated and recruited to the iNOS promoter in vivo via an IKKβmediated path way. As collagenous colitis is not associated with tissue injury, these data cha llenge the prevailing view that activation of NFκB per se mediates tissue injur y. Our results suggest that downstream inflammatory reactions leading to tissue damage originate in lamina propria immune cells, as increased NFκB activity in collagenous colitis was localised solely in epithelial cells, but present also i n macrophages in ulcerative colitis.
Background and aims: Expression of inducible nitric oxide synthase (iNOS) is gr eatly upregulated in the colonic mucosa of patients with collagenous and ulcerat ive colitis. As the transcription factor nuclear factor κB (NFκB) is a major i nducer of iNOS gene expression, we compared activation and transcriptional activ ity of NFκB in colonic mucosal biopsies from these patients. Methods: Eight pa tients with collagenous colitis, six with relapsing ulcerative colitis, and eight with uninflamed bowel were studied. Methods: NFκB DNA binding activity was asssed by In vivo recruitment of NFκB to the iNOS promoter was determined by chromatin immunoprecipitation analysis and transcriptional activity by NFκB gene expression profiling arrays. Cells show in g (IKK) activity by immunocomplex kinase assay. NFκB activation were identified by immunohistochemistry. Results: In collagen ous and ulcerative colitis, as op posed to uninflamed bowel, IKKβactivity and st rong NFκB DNA binding gave rise to activation of identical NFκB subunits and r ecruitment of transcriptionally active p65 to the iNOS promoter. In collagenous colitis, activated NFκB was observed only in epithelial cells while up to 10% of lamina propria macrophages showed activation in ulcerative colitis. Conclusions: In collagenous and ulcerative colitis, colonic mucosal NFκB is activated and recruited to the iNOS promoter in vivo via an IKKβmediated path way. As collagenous colitis is not associated with tissue injury, these data cha llenge the prevailing view that activation of NFκB per se mediates tissue injur y. Our results suggest that downstream inflammatory reactions leading to tissue damage originate in lamina propria immune cells, as increased NFκB activity in collagenous colitis was localized solely in epithelial cells, but also in macrophages in ulcerative colitis.